INTRODUCTION 



attraction with a force precisely equal thereto. But let 

 me beseech you to compare these two forces of lunar ac- 

 tion and reaction as denned by Newtonians to see 

 whether they are in any sense equal. Granting to the 

 moon an initial unearned momentum, that momentum is 

 nevertheless a finite quantity which can neither be in- 

 creased nor diminished of itself. If, therefore, it be 

 called upon to react against an extraneous force, it must 

 inevitably sacrifice some of its momentum, or, in other 

 words, lose some of its velocity. On the other hand, the 

 force it is pitted against, gravity, is a continuous force 

 which, however long drawn upon, loses not an iota of its 

 virtue. It can be shown that the attraction of the earth 

 upon the moon at their present distance is equal to some 

 240,000,000 million horse-power, for were she held for an 

 instant motionless in her orbit and then let go, it would 

 require that many horse-power to sustain her. In brief, 

 Newtonianism has dared to marry, in undivorcible union, 

 an imaginary, fortuitous, finite, unaugmentable and 

 wasting force to that of centripetal gravitation, which in 

 all things is precisely what the other is not. Astrono- 

 mers are by no means oblivious to this absurdity (al- 

 though they do not proclaim it from the housetops), as 

 is shown by their studied avoidance of Newton's word 

 "inertia" and the gratuitous substitution of the word 

 "persistence" in its place. 



Having now good-naturedly allowed ourselves to be 

 persuaded by our Newtonian teachers that the reason 

 why they have not succeeded in explaining translatory 

 motions is no fault of theirs, but of the motions them- 

 selves in being inexplicable per se, that nice adjustments 

 are so much matters of course that there is no need to 

 discuss them, and that persistent and inertial are inter- 

 changeable terms, we look forward expectantly for a 

 sweeping solution of all the riddles of the cosmos. Alas ! 

 only to be disappointed most grievously. Says Brew- 

 ster, writing about the year 1850 (M. of N., II, p. 313) : 



In concluding this brief notice of the progress of physical as- 

 tronomy since the time of Newton in a few of its leading features, 



